Method of and apparatus for reinforcing pipe

ABSTRACT

Reinforcing bands of high tensile strength filaments in a cured resin matrix are in the shape of a coil having a plurality of elastic convolutions for reinforcing a weakened pipe. Areas of depressions on the exterior surface of the pipe are filled with a load transfer filler material and the bands are coiled around the pipe with adhesive holding an innermost convolution of the coil to the pipe and subsequent convolutions of the coil to adjacent convolutions. A plurality of the bands are placed in abutment with one another to cover the entire weakened area of the pipe.

This is a Continuation of application Ser. No. 08/458,727 filed Jun. 2,1995, now abandoned, which is a continuation of application Ser. No.08/100,196 filed Aug. 2, 1993, now abandoned, which is a continuation ofSer. No. 07/493,357 filed Mar. 14, 1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to reinforcing pipe and, moreparticularly, to a method and apparatus for reinforcing pipe in apipeline which carries gas and/or liquid under pressure. The method andapparatus according to the present invention is especially useful inreinforcing a pipeline in service which has corroded or otherwisedeteriorated over time.

Pipelines for carrying gas or liquid under pressure are ordinarily madeof steel in order to with stand the fluid pressures necessary totransport fluids over large distances. Even though measures are takenduring the manufacture or installation of the pipe in the pipeline toprevent corrosion, corrosion occurs. Pipelines buried in the ground aresubject to deterioration from electrolytic and biochemical corrosion,cyclical soil stress, cathodic disbanding, and mechanical damage frommachinery used to install the pipeline or to expose, inspect and repairthe pipeline after installation. In addition, attachments to the pipe,such as valves, made of metal dissimilar to the metal of the pipe canresult in galvanic corrosion, as can damp soil. Over time, the pipesexhibit pits and dents.

Currently, the most common way of reinforcing a deteriorated pipeline isto detect areas of corrosion by means of a “smart pig” or cathodicsurveys, dig up the deteriorated regions of the pipeline, remove anycorrosion protection material which may have been placed around thepipe, clean the surface by shot-blasting, and apply a primer. Thepressure of fluid flow through the pipe is reduced, and split steelsleeves are welded or bolted onto the pipe. A plurality of the sleevesare installed end to end until the entire deteriorated area of thepipeline is covered. The pressure of the fluid is boosted to normal andthe pipeline buried.

Drawbacks of this process are that the steel sleeves are very heavy and,therefore, require cranes and several men to move them to the pipelineand into the proper position. The welding process is time consuming andrequires skilled workers. The sleeves are welded longitudinally andcircumferentially. The presence of longitudinal welds prevents thesleeves from providing a gas-tight or liquid-tight seal. Thecircumferential welds between the sleeves and having a high carboncontent create a heat effected zone in the pipe which is structurallyweakened.

The sleeves are intended to take up loading from the corroded portionsof the pipe. In order to transfer the load from the pipe to the sleeve,there must be a tight fit of the sleeve around the pipe. This isdifficult to achieve with sleeves because the pipes tend to becomedistorted and, when they do, the sleeves do not fit properly and must bepolished, that is, they must be ground to properly fit the pipe so as toadequately take up the load. Furthermore, there is a considerable amountof pipeline in and around oil refineries and tank farms where weldingcannot be done.

The present invention is directed to a method for restoring the burststrength of a pipe having an unbreached weakened region to at least thelevel for which the pipe was designed. For example, by the method of thepresent invention, the burst strength of a pipe having an unbreachedweakened region can be restored to a level at which the pipe canwithstand the forces of a pressure fluid in the pipe having a pressureof at least 500 pounds per square inch.

SUMMARY OF THE INVENTION

Through the use of the method and apparatus according to the presentinvention, a pipeline can be reinforced without removing the pipelinefrom service, without using cranes or other heavy equipment for movingthe reinforcement into position, and without employing welding or othertime consuming procedures. the pipeline can also be reinforced withoutthe application of heat which would cause weaknesses in the pipe andpresent a hazard to safety and without the need for skilled labor.

The present invention achieves these advantages through the use of bandsof elongate unidirectional, lightweight, non-metallic, high tensilestrength filaments in a resin matrix cured to form a strip in the shapeof a coil similar to a clock spring, wherein the coil has an elasticmemory. Although the coil has a continuously changing radius ofcurvature, the coil bands for a pipe of predetermined outer radius arechosen so that the radii of all portions of the coil band are smaller inthe relaxed state of the band than the outer radius of the pipe, sothat, when the bands are wound around the pipe, the elastic memory orset in the convolutions of the bands helps maintain the bands in contactagainst the pipe, for the first convolutions, and in contact with theunderlying convolutions for the later convolutions. Because the resinmatrix for the filaments is already cured at the time of installation,there are no fumes associated with the matrix during the installation ofthe bands. The problem is especially acute since work usually must beperformed in a ditch where any fumes would accumulate. Furthermore, workoften must be performed in adverse climatic conditions in which uncuredresins will not work properly.

In order to reinforce an existing pipeline, the earth is dug out aroundand under the pipeline, as is conventionally done, and the surface ofthe pipe in the pipeline is prepared in a conventional manner.

The coil bands are carried manually to the pipe and manually supportedand wound around the pipe, most efficiently by a two-person team. Foreach band, the outer end of the coil is secured to the pipe by anadhesive pad, and the band is unwound from the coil and onto the pipe asthe coil is moved around the pipe. The pipe is coated with a layer ofadhesive, for example, with a paint roller or brush or by spraying, andthe coil is moved around the pipe. A coating of the adhesive is appliedto the outer surface of each convolution of the band as the band iswound around the pipe so that a continuous layer of adhesive is definedbetween adjacent convolutions of the band. When the band is completelyunwound from its coil and onto the pipe, it forms a new coil, invertedwith respect to the original coil. The next band is brought intoposition and installed in the same manner, so that its edges abut theedges of the first reinforcing band. The bands are in intimate contactwith the pipe, either directly or through the load transferring fillermaterial, by which the load on the pipe is transmitted to the bands. Asa result, the bands reinforce the pipe, preventing the pipe from bulgingdue to stresses too great for the weakened metal alone and therebypreventing failure of the pipe. Coil bands having a plurality of,typically about five, convolutions provide the deteriorated pipe withgreater burst strength than it had when it was new, allowing the pipe towithstand up to twice the bursting pressure where the wall of the pipeis completely reinforced with the bands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a pipe having a steel sleeve welded aroundit to provide reinforcement in a known manner;

FIG. 2 is an enlarged fragment of a cross section of a pipe showing arepaired region of deterioration;

FIG. 3 is a perspective view of a coil reinforcement band according tothe present invention;

FIG. 4 is a view of a coil reinforcement band being installed around apipeline in a ditch;

FIG. 5 is a fragmentary front view of a pipe on which a plurality ofcoil reinforcement bands according to the present invention have beenplaced to provide reinforcement, portions of some of the bands being cutaway;

FIG. 6 is a transverse cross section of the pipe of FIG. 5 taken alongthe line 6—6; and

FIG. 7 is an enlarged fragment of the cross section of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A common way of reinforcing a pipe in the field is to detect areas ofdeterioration, dig up the deteriorated areas, remove any corrosionprotection material, clean the surface, and apply a primer. The flow offluid through the pipeline is reduced and, as can be seen from FIG. 1,sections of a split steel sleeve 2 having an internal diameter justslightly larger than the outer diameter of the pipe 1 are placed aroundthe pipe until they cover the deteriorated region which is to bereinforced. The sleeve 2 is welded to the pipe 1 circumferentially atthe ends of the sleeve, the welding beads being designated by thereference numeral 3. Additional, longitudinal welding beads (not shown)secure the sections of the split sleeve to one another. The heat ofwelding of the beads 3 results in regions 4 of embrittlement in the pipecausing a structural weakening of the pipe.

The first step in reinforcing a pipeline in accordance with the presentinvention is the detection of corrosion or other weakness. This is doneconventionally by cathodic surveys or by sending a smart pig through thepipe which is capable of detecting the presence and location of theweakness. After the areas of corrosion have been determined, theportions of the pipeline containing the weakened areas are exposed byexcavating along the sides of and underneath the pipeline.

Pipelines ordinarily have corrosion protection, typically in the form ofcoal tar or tape or thin film epoxy. The corrosion protection has atendency to become damaged, and, when it does, corrosion occurs. Beforereinforcing can be done, coal tar must be removed by “chipping” most ofthe coal tar and scraping off any of the coal tar which does not comeoff by chipping. The removal of the coal tar or other corrosionprotection reveals the regions of corrosion, such as the region 5 ofpits shown in FIG. 2, which leave the surface of the pipe 1 in a rough,irregular condition. Mechanical damage such as dents may also bepresent.

In the method of reinforcing the pipe according to the presentinvention, the pipe 1 is sandblasted to prepare the surface for a newcorrosion protection layer 6. One suitable corrosion protection materialis a two-part epoxy available from Celicote, Inc. under the nameFlakeline 252. This material calls for the underlying surface to bewhite metal with an anchor pattern, a known surface standard whichallows protective coatings to adhere properly. A pretreat bond primer isapplied to the dents and areas of pitting caused by the corrosion, and afiller material 7 is applied on top of the primer to fill in the pitsand provide the pipe 1 with a smooth outer surface having a constantdiameter. A suitable filler material is a two-component epoxy availableunder the trade name Koppers Splash Zone Compound #A-788. The fillermaterial 7 serves to transfer the load, that is, the forces applied tothe pipe 1 by the pressure fluid inside the pipe, to the reinforcementyet to be installed. When the filler material 7 has cured, a layer ofcorrosion protection material 6 is applied to the filled-in regions ofthe pipe 1, as well as to adjacent regions which did not require fillingin. The corrosion protection material 6 can be a conventional shrinksleeve, tape or mastic.

An adhesive 9 (FIG. 7) is applied by a conventional paint roller to theentire surface of the pipe 1, on top of the corrosion protectionmaterial 6. A suitable adhesive is a one component, moisture-activatedurethane adhesive. An active ingredient in the adhesive causes afrothing and CO₂ outgassing between the coil reinforcement band 10 andthe underlying surface, which is the corrosion protection layer 6. MobayBaytec B-90 is a suitable adhesive.

As can be seen from FIG. 3, the coil reinforcement band 10 comprises acoil web of composite material having a rectangular cross section, aninner surface, an outer surface, and side or edge surfaces. The band 10has a plurality of concentric elastic: convolutions including aninnermost convolution having an inner end 12, an outermost convolutionhaving an outer end 14, and intermediate convolutions. The compositematerial includes a large plurality of lightweight, high tensilestrength, electrically non-conductive nonmetallic fibers extendingparallel to one another along the length of the web, the fibers beingencapsulated in a cured resin matrix. Although the parallel fibers aregenerally indicated in FIG. 3 by parallel longitudinal lines 16, eachspace between adjacent parallel lines 16 actually represents hundreds orthousands of longitudinal fibers, each having a diameter, in the case ofE-type glass fibers, of less than 0.001 inch.

The longitudinal fibers may be held together by cross threads 18, whichcan facilitate the application of the resin matrix to the fibers duringmanufacturing prior to curing. With the cured resin in place, thecomposite material is impervious to soil corrosion and most fluid and,thereby, protects the fibers and the portion of the pipe 1 underlyingthe coil reinforcement band 10 from corrosion. Glass is a suitablematerial for the fibers and especially E-type glass fibers, because theyare relatively inexpensive. Other fibers, such as fibers made of Kevlar,may also be used. Suitable resins are elastic when cured, therebyexhibiting an elastic memory, and, when they are cured in a coiled coilconfiguration as in the coil reinforcement band 10, the resins willcause the band 10 to return to the same coil configuration after beinguncoiled, once the uncoiling force is removed. Like the fibers, theresins are electrically non-conductive, thereby enabling the coilreinforcement bands 10 to preserve the cathodic corrosion protection ofthe pipe. Polyester, polyurethane or epoxy resins can be used.

As can be seen from FIG. 4, after the pipe 1 has been properly prepared,an adhesive pad 8, having a contact adhesive on both sides, is attachedto the pipe 1, on top of the corrosion protection material 6. Arectangularly shaped closed cell vinyl pad of 3½ inches by 9¼ inches hasbeen found to work well. In FIG. 4, the reinforcement band 10 is beingapplied to a pipe 1 which is a part of a pipeline. The portions of thepipeline which require reinforcement are exposed by digging a ditch 22.No cranes or other equipment are required to move the reinforcementbands 10 to the pipeline or support the bands during installation on thepipe. Due to their light weight, the bands 10 can be carried andpositioned manually, usually by one person. The weight of a coilreinforcement band 10 for a 16 inch diameter pipe, for example, is 14pounds, and for a 30 inch diameter pipe, the weight is 29 pounds.

The inner end 14 of the coil reinforcement band 10 is applied to thepipe 1 at the reference point by the adhesive pad 8. After the first endis attached to the pipe 1, the band 10 is uncoiled from its coil bymoving the band over and under the pipe 1, and uncoiling the coil as itis moved around the pipe. This process is continued until the trailingend of the band 10 is brought into contact with underlying convolutionsof the band and secured by, for example, fiber tape. Care should betaken with the first band 10 to assure that its edges are transverse tothe longitudinal axis of the pipe 1 so that the first band 10 can serveas an alignment band for adjacent coil reinforcement bands 10 to beinstalled next, as can be appreciated from FIG. 5. In the embodiment ofthe invention illustrated in FIG. 5, the corrosion protection material6, in the form of a shrink wrap (shown in cross section), can be placedover the bands 10, encapsulating the bands and the pipe, as analternative to the corrosion protection being placed between the bands10 and the pipe 1.

As can be seen from FIG. 7, after the first convolution is applied tothe pipe 1, the outer surface of the convolution is coated with theadhesive 9 for the reception of the next convolution, and then thatconvolution is coated with the adhesive, and so on, until the finalconvolution is reached. The final convolution need not be coated. Theadhesive coating 9 of each convolution is sprayed with water, or acatalyst activated with water, for activation of the adhesive before thenext convolution is brought into contact with the adhesive. One or morebands of tape, for example, fiber tape, are placed around thereinforcement band 10 to hold the band 10 tightly in place until theadhesive 9 cures.

Although FIG. 4 shows a single person in the ditch 22, a two-person teamis advantageous for applying the coil reinforcement bands, since eachperson can pass the coil over or under the pipe to the other person asthe band is applied. In addition, each person can hold the remainingcoil and maintain tension in the convolution being applied to the pipeto assure a tight fit, while the other person applies the adhesivecoating to the external surface of the convolution. Upon wateractivation and curing, the adhesive permeates any gaps in the coil bandsaround the pipe and forces trapped oxygen to the surface, bonding theband permanently to the pipe, and the convolutions of the band to oneanother. The oxygen is converted to carbon dioxide through the reactionof the water and, thereby, eliminated. Without oxygen, the corrosionwill not take place.

In order to evaluate the effectiveness of the coil reinforcement bands10 as a pipeline reinforcement on a large diameter gas transmissionpipe, two 20 foot 5LX56 DSAW pipes approximately 25 years old and takenout of natural gas service some years previously were tested. The pipeseach had a 30 inch diameter and a 0.375 inch wall thickness. Each pipehad spot corrosion. The first pipe, which was tested without anyreinforcement, had three major corrosion areas having pit depth rangesas follows:

Group 1: .055″-.100″ Group 2: .045″-.090″ Group 3: .085″-.120″

The second section had ten areas of corrosion, the corrosion beingsubstantially more severe than that of the first pipe. The pit depthranges were as follows:

Group 1: .075″-.100″ Group 2: .060″-.100″ Group 3: .060″-.100″ Group 4:.110″-.230″ Group 5: .100″-.170″ Group 6: .085″-.140″ Group 7: .140″Group 8: .080″-.160″ Group 9: .105″-.112″ Group 10: .090″-.120″

Twenty-one coil reinforcement bands 10 were applied to the second pipe,the bands 10 being in abutment with one another, covering all of thecorroded areas, and covering substantially the entire length of thepipe. Prior to the application of the coil reinforcement bands 10, theentire second pipe was wire brushed, and the corroded areas were wirebrushed a second time to eliminate all loose rust particles. The fillermaterial 7 was applied in the pitted areas to provide force or loadtransfer from the wall of the pipe to the reinforcement bands 10. Theurethane adhesive was applied and activated with water.

Headcaps were welded onto the ends of both pipes so that the pipes couldbe pressurized. The first pipe, the bare pipe, was placed in a test pitand filled with water. The water pressure was gradually increased with a4 gallon per minute, three piston, 4,000 p.s.i., 10 horsepowerhydrostatic pump. At 2,172 p.s.i., the pipe ruptured in the sidewallnear the deepest pit grouping of that pipe, Group 3, which was0.085″-0.120″ in depth.

The second pipe, the pipe reinforced with the coil reinforcement bands10, was placed in the test pit and similarly pressurized with water. Ata pressure of 2,463 p.s.i., the pipe failed, not in the reinforcedregion, but at the juncture where one of the headcaps was welded to theend of the pipe. It is believed that the reason for the prematurefailure was due to an accelerated cooling rate of the steel under theconditions of welding, producing a heat affected zone which led to thefailure.

A new welding procedure was developed which required the removal of onereinforcement band at each end of the pipe. After the headcaps werewelded to the ends of the pipe by the new procedure, the pipe was againplaced in the pit and pressurized with water. This time, the pipe didnot fail until the water reached a pressure of 3,635 p.s.i., at whichpoint the pipe failed adjacent to its long seam weld.

Similar tests were conducted on 16 inch, 24 inch and 36 inch pipes, withsimilar results.

A latitude of modification, change and substitution is intended in theforegoing disclosure. Accordingly, it is intended that the appendedclaims be construed broadly and in a manner consistent with the spiritand scope of the invention therein.

What is claimed is:
 1. A method for restoring the burst strength of apipe having an unbreached weakened region to a level at which the pipecan withstand the forces of a pressure fluid in the pipe having apressure of at least 500 pounds per square inch, the weakened regioncomprising at least one depression in the outer surface of the pipecomprising: detecting the weakened region; providing a load-transferringfiller material; filling the depression with the filler material; andwrapping around the pipe in the weakened region a strip of high tensilestrength material comprising unidirectional high tensile strengthfilaments in a cured resin matrix and defining a coil band having alength, an inner surface, an outer surface, opposite side surfaces and aplurality of elastic convolutions, the filaments extending parallel tothe length of the coil band, the step of wrapping including placing afirst elastic convolution around the pipe and placing subsequent elasticconvolutions around underlying convolutions on the pipe such that theopposite side surfaces of the band in said subsequent elasticconvolutions are in radial alignment with opposite side surfaces of theband in the underlying convolutions, the step of wrapping furtherincluding securing the convolutions from movement so that theconvolutions do not move relative to one another when the pipe ispressurized, whereby the wrapped pipe has a burst strength of a level atwhich the pipe can withstand the forces of a pressure fluid in the pipehaving a pressure of at least 500 pounds per square inch.
 2. The methodaccording to claim 1, wherein the high tensile strength filaments arenonmetallic.
 3. The method according to claim 2, wherein the nonmetallicfilaments comprise glass fibers.
 4. The method according to claim 3,wherein the glass fibers comprise E-type glass fibers.
 5. The methodaccording to claim 1, wherein the step of wrapping comprises wrapping aplurality of said strips around the pipe such that the strips cover theweakened region.
 6. The method of claim 1, wherein the step of wrappingfurther includes securing the first elastic convolution to the pipe withan adhesive.
 7. The method of claim 1, wherein the convolutions aresecured from movement relative to one another by an adhesive.
 8. Themethod of claim 7, wherein the convolutions are secured from movementrelative to one another by a coating of adhesive defining a continuouslayer between adjacent convolutions of the band.
 9. The method of claim7, wherein the adhesive is a urethane adhesive.
 10. The method of claim9, wherein the urethane adhesive is moisture activated.
 11. The methodof claim 7, wherein the convolutions are secured from movement relativeto one another by applying adhesive to an outer surface of each of theconvolutions of the band except the outermost convolution.
 12. Themethod of claim 1, wherein the method restores the burst strength of thepipe to a level at which the pipe can withstand the forces of a pressurefluid in the pipe having a pressure of at least 1000 pounds per squareinch.
 13. The method according to claim 1, wherein the step of wrappingfurther includes applying tension tangentially to the convolutions toplace the coil band tightly in engagement with the filler material. 14.The method according to claim 1, further comprising applying an adhesivebetween the filler material and the coil band.
 15. A method forrestoring the burst strength of a pipe in a pressure fluid transmissionpipeline, the pipe having an unbreached weakened region, to et least thelevel for which the pipe was designed, the weakened region comprising atleast one depression in the outer surface of the pipe, comprising:detecting the weakened region of the pipe in the pressure fluidtransmission pipeline; providing a load-transferring filler material;filling the depression with the filler material; and wrapping around thepipe in the weakened region a strip of high tensile strength materialcomprising unidirectional high tensile strength filaments in a curedresin matrix and defining a coil band having a length, an inner surface,an outer surface, opposite side surfaces and a plurality of elasticconvolutions, the filaments extending parallel to the length of the coilband, the step of wrapping including placing a first elastic convolutionaround the pipe and placing subsequent elastic convolutions aroundunderlying convolutions on the pipe such that the opposite side surfacesof the band in said subsequent elastic convolutions are in radialalignment with opposite side surfaces of the band in the underlyingconvolutions, the step of wrapping further including securing theconvolutions from movement so that the convolutions do not move relativeto one another when the pipe is pressurized.
 16. The method of claim 15,wherein the step of wrapping further includes securing the first elasticconvolution to the pipe with an adhesive.
 17. The method according toclaim 15, wherein the step of wrapping further includes applying tensiontangentially to the convolutions to place the coil band tightly inengagement with the filler material.
 18. The method according to claim15, further comprising applying an adhesive between the filler materialand the coil band.
 19. The method according to claim 18, wherein theadhesive is a moisture-activated urethane adhesive.
 20. The methodaccording to claim 15, wherein the high tensile strength filaments arenonmetallic.
 21. The method according to claim 20, wherein thenonmetallic filaments comprise glass fibers.
 22. The method according toclaim 21, wherein the glass fibers comprise E-type glass fibers.
 23. Themethod according to claim 15, further comprising wrapping a plurality ofsaid coil strips around the pipe such that the coil bands cover theweakened region.
 24. The method according to claim 23, comprisingpositioning the strips with side surfaces of the bands defined by thestrips in abutment with one another.
 25. The method of claim 15, whereinthe convolutions are secured from movement relative to one another by anadhesive.
 26. The method of claim 25, wherein the adhesive is a urethaneadhesive.
 27. The method of claim 26, wherein the urethane adhesive ismoisture activated.
 28. The method of claim 25, wherein the convolutionsare secured from movement relative to one another by applying adhesiveto an outer surface of each of the convolutions of the band except theoutermost convolution.
 29. The method of claim 25, wherein theconvolutions are secured from movement relative to one another by acoating of adhesive defining a continuous layer between adjacentconvolutions of the band.
 30. The method according to claim 11, whereinthe high tensile strength filaments are electrically non-conductive.